The carburetor is a device that mixes air and fuel for an internal combustion engine. The majority of motorcycles and many snowmobiles and outboard motors still are carbureted due to lower weight and cost compared to fuel-injected engines. Some carbureted engines have a single carburetor, though the modern trend is to use multiple carburetors, of two to eight carburetors. The carburetor works on Bernoulli's principle, which is that moving air has lower pressure than still air, and that the faster the movement of the air, the lower the pressure. The throttle or accelerator controls the amount of air that flows through the carburetor. Faster flows of air entering the carburetor draws more fuel into the carburetor due to the partial vacuum that is created. To function correctly under all conditions, most carburetors require tuning, and for engines with multiple carburetors, it is important that the carburetors be tuned together to provide balanced performance.
A manometer is a pressure measuring instrument which is typically used when adjusting carburetors, whether single or multiple. It uses a column of liquid whose height in a glass tube indicates the pressure which is applied to the openings of the tube. Manometers can be of the type referred to as an “open-end manometer” which is generally “U-shaped” and has both ends open. One of the open ends is typically open to atmospheric pressure and the other end is then connected to a pressure source to be measured. By comparing the levels in the two legs of the U structure, the pressure of the pressure source can be measured compared to atmospheric pressure.
The second type of manometer in common use is referred to as a “closed-end manometer”, where one end is closed and thus a vacuum source connected to the open end pulls against the liquid in the closed tube. This generally gives a measurement of pressure which is lower than atmospheric pressure.
When using manometers or other pressure measurement devices in tuning multiple carburetors in a vehicle, the goal is generally to have the air flow (and thus pressure) in each of the carburetors match as closely as possible to each other. Since it is the relative pressure in each carburetor with respect to each other that is important, the absolute pressure in each channel is not usually a concern. Thus, the purpose of using a manometer for pressure measurement is generally to equalize the pressures in all of the carburetors. It may be possible to do this with a single channel manometer, by noting the pressure in a first carburetor and then connecting the single channel manometer to each successive carburetor in turn, but this is a time consuming and inefficient method because carburetor adjustments affect engine performance and engine performance affects the pressure of previously adjusted carburetors, so it would have to be an iterative process, which would be very time consuming and with less assurance of success. It would be easier and more efficient to be able to monitor all carburetors simultaneously, especially in cases where there may be some cross-effect, whereby the adjustment of a second carburetor affects the performance of the first.
Additionally, it would be an advantage if the fluid-level line in each of the channels of a multi-channel manometer could be individually adjusted, so that there would be maximum flexibility in the calibration of the multi-channels with respect to each other and to a pressure source, such as one of the carburetors in a multi-carburetor engine.
Thus, there is a need for a multi-channel manometer with independent channel fluid-level adjustments for calibration.